diff --git a/esphome/config_validation.py b/esphome/config_validation.py
index fa2a14dbd6..1319786841 100644
--- a/esphome/config_validation.py
+++ b/esphome/config_validation.py
@@ -838,9 +838,16 @@ def percentage(value):
 
 
 def possibly_negative_percentage(value):
-    has_percent_sign = isinstance(value, str) and value.endswith('%')
-    if has_percent_sign:
-        value = float(value[:-1].rstrip()) / 100.0
+    has_percent_sign = False
+    if isinstance(value, str):
+        try:
+            if value.endswith('%'):
+                has_percent_sign = False
+                value = float(value[:-1].rstrip()) / 100.0
+            else:
+                value = float(value)
+        except ValueError:
+            raise Invalid("invalid number")
     if value > 1:
         msg = "Percentage must not be higher than 100%."
         if not has_percent_sign:
diff --git a/tests/test3.yaml b/tests/test3.yaml
index 53bbdf023c..dded01fb67 100644
--- a/tests/test3.yaml
+++ b/tests/test3.yaml
@@ -14,6 +14,8 @@ esphome:
 substitutions:
   devicename: test3
   devicecomment: test3 device
+  min_sub: "0.03"
+  max_sub: "12.0%"
 
 api:
   port: 8000
@@ -769,6 +771,8 @@ servo:
   id: my_servo
   output: out
   restore: true
+  min_level: $min_sub
+  max_level: $max_sub
 
 ttp229_lsf: